I feel in the case of Hancock it's a way more interesting story for her secret to be outed and she having to confront her worst fears. It's a classic setup that leads to character development and a personal arc with fall and ascension.
She's already confronted her worst fears, though - that's the entire point of her character arc in Amazon Lily.
I'm not going to say that the Boa sisters aren't afraid of being sent back into slavery, because that's not true, but their greatest fear was always that someone would find out their secret. They built up a legend of being cursed by a gorgon to try to keep their backs hidden from view, because they believed that if knowledge of their slave brands were ever to become known, then everything they'd built up since gaining their freedom would collapse. That their people would lose faith and abandon them, and that for all their strength, they'd be left as nothing more than the same traumatized slave girls they had once been.
Hancock spent her entire adult life unable to trust anyone but her sisters and the handful of elders (Nyon, Rayleigh, etc.) that helped them get back on their feet after regaining their freedom. She was constantly afraid that her secret would be used against her if it were known, but when Luffy found out, not only did he not treat them any differently, he also recognized it was a sore point for them and acted to help them keep it secret even when it didn't benefit him. In Luffy she found someone she could place her trust in who would not betray it, and while her instantaneous transformation into a lovesick schoolgirl gets most of the focus, I think the realization that maybe she COULD place her trust in others without it being taken advantage of is of equal importance.
She keeps up the "Ice Queen" persona for dealing with the World Government, but she's become a better, more confident, vastly more approachable leader for her people now. I wouldn't be surprised if there are more in Hancock's inner circle who've been brought into the loop over time, because ironically, the Boa sisters' past as slaves matters most when no one knows about it. The more of their people in the know who support them anyway, the less it can be used against them and the less they have to fear from it being revealed. Hancock's secret only had power over her because she allowed it to, and I think the point of her arc since her introduction was in moving her psychologically to a place where she doesn't have to be afraid of it anymore.
You seem to think she isn't there yet and requires another round of imprisonment, enslavement, and emancipation in order to reach that point. I think that such an arc would only serve to roll back her existing character development, because I believe she's more or less there already.
